We like Empo-ni - they are a small company that is at the cutting edge of renewable energy technology, and their small and efficient SOL1 regulator is nicely made and has some great features.
The SOL1 is suitable for use with any solar panel up to 100W, and works on both 12V and 24V power systems - it automatically detects the battery bank voltage. Uniquely, it can convert the voltage of a 12V solar panel up to 24V - no need to have a pair of panels wired in series any more if your battery bank is 24V. However, it does work equally well on 12V battery systems.
On average you will get around 15-20% more power from your solar panel using a SOL1 compared to a conventional regulator. But when it really matters - in dull, overcast conditions, or when your battery is flat - the increase in output can be as much as 30%.
Comes with a battery status LED - for more information on charging currents etc we suggest the use of a batttery monitor such as the NASA BM-1.